The human gut hosts millions of bacteria, which harmoniously balance the immune system, help digest food, produce vitamins, and promote gastrointestinal (GI) motility. Loss of homeostasis in the gut may contribute to an imbalance associated with disease states, such as immune and neurological disorders, and cause GI problems, which can exacerbate other disorders or symptoms. For example, Autism Spectrum Disorders (ASDs) are complex neurobiological disorders whose chief manifestations are qualitative impairment in social interaction and communication and restricted repetitive and stereotyped patterns of behavior, interests, and activities. There has been a world-wide increase in the diagnosis of ASD, which has reached epidemic level. ASD subjects and their families face difficulties in treatment because ASD does not share a common etiology. Both genetic and environmental factors are important in the etiology of autism, with a recent large twin concordance study suggesting that environmental factors are at least as important, if not more important, than genetic ones. A potentially important environmental factor is abnormal intestinal flora that often interacts with other factors such as intestinal permeability and transport of toxic substances. Hence, there remains a need for understanding the role of the microbiome in the healthy gut versus the unhealthy gut, and, in particular in the context of ASD subjects.